Walmart challenges Amazon Prime

NEW YORK (CNNMoney) -- Walmart Stores is rolling out an unlimited shipping service that could undercut Amazon Prime.

Walmart said it will offer a subscription delivery service this summer for $50 a year, roughly half the price of Amazon Prime, with its annual fee of $99.

The discount chain said the products would arrive within three days.

"Frankly we're surprised it took Walmart this long to launch any sort of loyalty program," wrote Matt Nemer, senior analyst for Wells Fargo, in a note to investors, where he mentioned the success of buy-in memberships with Amazon and Costco.

"While we're encouraged Walmart is jumping into the mix, Walmart will have heavy lifting ahead to catch up with Prime, which we believe will continue to push the envelope on shipping speed and add new services," he said.

Walmart currently has an online ordering system that offers free shipping for orders that are $50 or more. Amazon has a better deal, with free shipping on orders over $35.